The establishment of an adequate airway is the first critical step in the resuscitation of a seriously ill or injured patient. Tracheal intubation is the preferred method for establishing an adequate airway in these circumstances. There are both a standard method of endotracheal intubation and several experimental systems. Conventional endotracheal intubation consists of the passage of a tube into the trachea. This conventional tube is open at both ends and contains a standard 15 mm adapter for attachment of a conventional bag valve or other conventional resuscitation device. When an inflatable membrane or cuff located near the end of the endotracheal tube is inflated, the airway is sealed. This allows intermittent positive pressure ventilation to be carried out and protects the airway from aspiration of foreign material. The current standard method involves the use of a malleable stylet which is inserted into the endotracheal tube so that the tube will conform to the desired configuration. The end of the stylet must always be recessed at least 11/2 inches from the tube opening to prevent trauma during intubation. A laryngoscope is then employed to achieve visualization of the glottis and vocal chords, followed by insertion of the endotracheal tube with stylet through the vocal chords and into the trachea.
The laryngoscope is a device used for exposure of the glottis. It consists of a blade and handle. The handles are interchangeable, and the blade may be curved or straight. The head is then positioned to obtain the proper orientation with respect to the neck. Three axes, those of the mouth, the pharynx, and the trachea, must be aligned with respect to each other to achieve direct visualization of the trachea. In order to accomplish this objective, the neck must be flexed forward and the head must be extended backward. This puts the head into a "sniffing" position. The head must not be allowed to hang over the end of a bed or table. At the very least the occiput of the head should be on the same horizontal plane as the back of the shoulders, with the neck somewhat elevated. In most cases, it is helpful to place a few layers of toweling under the occiput to elevate it a few inches above the level of the bed. The blade of the laryngoscope is then inserted into the mouth following the natural contour of the pharynx. Once visualization of the glottic opening has been achieved with the laryngoscope the endotracheal tube is directly inserted into the larynx and trachea. In order to accomplish this maneuver, it is necessary to place the laryngoscope blade either under the epiglottis or into the space between it and the base of the tongue. A laryngoscope is employed by exerting traction upward on its handle, displacing the base of the tongue and the epiglottis anterially and exposing the glottic opening. In the process of this exposure the entire laryngoscope is pulled in a perpendicular direction directly away from the patient's head, with considerable attendant stress to the surrounding tissue in the head and the spine of the patient. Upon visualization of the epiglottis the endotracheal tube is passed between the vocal chords anterior to the arytenoid cartilages.
In emergency endotracheal intubation, with its attendant risk of regurgitation and aspiration of gastric contents, the Sellick Manoeuver is employed to apply firm pressure over the cricoid cartilage in order to occlude the upper end of the esophagus. An assistant applies firm backward pressure to the cricoid until intubation has been completed and the endotracheal tube cuff inflated.
Tracheal intubation achieves total control over the airway. This protects the airway from aspiration of foreign material and allows for intermittent and positive pressure ventilation with 100% oxygen. It makes the trachea and the respiratory tract available for suctioning. It further eliminates the problems of gastric distention associated with mouth-to-mouth or bag-valve mask ventilation. The disadvantages of this standard method are several. It requires a physician skilled in endotracheal intubation in a situation where one is not always available, or where she may be otherwise occupied with other life saving procedures on the patient. Also the present method takes several minutes, even in the hands of a skilled physician, and too often results in trauma to the tracheal and pharyngeal tissues as well as sometime intubation of the esophagus and stomach resulting in dangerous vomiting. In the standard method it is necessary to auscult the chest as soon as possible after intubation to make certain that the lungs are being ventilated. The epigastric area may be auscultated after a tracheal intubation and after chest auscultation to confirm that the tube is in the trachea and not in the esophagus, which would require reintubation. In addition there is risk of injury to the spine, particularly where there are already attendant spinal injuries. Finally anatomic distortions, either congenital or caused by the injuries, may further hamper or completely frustrate the use of the standard method.
The experimental systems all require retrograde nasal or oral insertion of an endotracheal tube along a guide wire. The experimental systems all require insertion of a hollow core needle percutaneously into the intracrycoid space of the trachea. A guide wire is then inserted translaryngially through the hollow needle in the intercrycoid space through the trachea, superiorly up through the pharynx and out of the mouth or nose. There follows then a guided insertion of a standard endotracheal down the guide wire into the trachea. The guide wires employed in current experimental methodology all employ some kind of flexible configuration at the inserted end of the guide wire, while the retained end of the guide wire at the intercrycoid insertion site remains stiff and unused. In known experimental methods, once the guide wire is advanced into the oral pharynx it is either allowed to pass fortuitously out of the mouth or nose or else it is retrieved with forceps. The guide wire is then pulled out through the mouth or nose to a length which is greater than the length of the endotracheal tube to be used. Typically, the hollow needle is removed after the guide wire with its flexible superior tip has been inserted into the trachea. One experimental method calls for the insertion of the guide wire into the lumen, or side hole, of the standard endotracheal tube in order to minimize "wandering" of the tube as it progresses inferiorally through the pharyngeal cavity and down towards the glottic opening into the trachea to the point of the needle's insertion. This positioning of the guide wire in the lumen also allows the insertion of the endotracheal tube an extra centimeter or so beyond the point of the guide wire's intercrycoid insertion. At this point in all of the experimental methods, the guide wire is then removed. In some methods the endotracheal tube is then further advanced into the trachea. Once at an appropriate position the circumferential balloon or inflatable cuff of the endotracheal tube is inflated and the patient is intubated.
These known experimental methodologies call for a large diameter, relatively inflexible, endotracheal tube to be advanced over a small diameter, relatively flexible, guide wire down into the trachea. The guide wire remains inserted in the intracrycoid transit site, and is even used as leverage point to assist in the advancement of the endotracheal tube. There are several disadvantages of these current experimental intubation systems.
First, it is difficult to locate and retrieve the end of the currently employed guide wires in the oral pharynx because of the size of the guide wire and the lack of direct visualization. These problems may be exacerbated in emergency situations.
Second, the advancement of the endotracheal tube over the guide wire and stiff nature of the retained end of the guide wire at the tracheal insertion point of the wire create significant leverage pressure upon the tissue at the guide wire's intracrycoid insertion point because the point acts as a fulcrum during the advancement procedure. This can cause significant trauma to the tissue surrounding the insertion point, such as tearing or hemorrhaging, trauma which can be especially severe as a result of excessive advancement of the endotracheal tube beyond the point of insertion during rapid emergency procedures because the guide wire is then forcibly thrust downwardly against delicate tissue. This excessive advancement can and does easily occur in these emergency situations.
Third, even with a lumen or side hole insertion of the guide wire into the endotracheal tube, and especially without such insertion, the relatively large diameter endotracheal tube is allowed to float significantly from the guide wire's path during intubation, and this "wandering" can cause significant trauma to various tissues in the pharyngeal and laryngeal paths, particularly to the vocal chords. Occasionally the trauma can be so severe as to result in obstruction of the endotracheal tube's passage into the trachea.
Fourth, the conventional endotracheal tube is both blunt and stiff on its advancing inferior end and that bluntness and stiffness can also result in significant trauma to surrounding tissues and structures, primarily to the vocal chords, as the endotracheal tube is advanced.